Field of the Invention
The present invention relates to a fuel cell stack formed by stacking a plurality of fuel cells. Each of the fuel cells is formed by stacking a membrane electrode assembly and a separator together. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes.
Description of the Related Art
For example, in a solid polymer electrolyte fuel cell, a polymer ion exchange membrane as an electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly make up a power generation cell for generating electricity. In use, a predetermined number of power generation cells are stacked together to form a fuel cell stack, e.g., mounted in a vehicle.
In the fuel cell, a fuel gas flow field for supplying a fuel gas to the anode and an oxygen-containing gas flow field for supplying an oxygen-containing gas to the cathode are formed in surfaces of separators. Further, a coolant flow field is formed between adjacent separators for supplying a coolant along the surfaces of the separators.
At least fluid passages such as a fuel gas supply passage for supplying the fuel gas to the fuel gas flow field and a fuel gas discharge passage for discharging the consumed fuel gas from the fuel gas flow field are formed in an end plate provided at one end in the stacking direction. Further, fluid passages such as an oxygen-containing gas supply passage for supplying the oxygen-containing gas to the oxygen-containing gas flow field and an oxygen-containing gas discharge passage for discharging the consumed oxygen-containing gas from the oxygen-containing gas flow field are formed in the end plate.
This internal manifold type fuel cell is connected to external equipment such as a humidifier for humidifying the oxygen-containing gas and the fuel gas before the gases are supplied to the fuel cell. In this regard, in most cases, external pipes provided in the external equipment have a cylindrical shape. On the other hand, fluid passages formed in the end plate have a rectangular or triangular (non-circular) shape. Therefore, it is difficult to connect the circular external pipes to the non-circular fluid passages in an air-tight manner.
As a fuel cell stack aimed to address the problem, a fuel cell stack disclosed in Japanese Laid-Open Patent Publication No. 2009-224194 (hereinafter referred to as the conventional technique 1) is known. In the fuel cell stack, resin connection pipes are provided at one of end plates to connect non-circular passages and circular external pipes. Each of the resin connection pipes includes a non-circular cylindrical portion connected to the non-circular passage, a circular cylindrical portion connected to the circular external pipe, and a cylindrical portion having a connector shape connecting the non-circular cylindrical portion and the circular cylindrical portion in the thickness direction of the one of the end plates.
Further, in the internal manifold type fuel cell, piping structure is adopted for connecting the fluid passages and the external equipment. As a technique of this type, for example, piping structure of a fuel cell stack disclosed in Japanese Laid-Open Patent Publication No. 2006-228632 (hereinafter referred to as the conventional technique 2) is known.
In the piping structure, as shown in FIG. 17, a fuel cell stack 2 for generating electrical energy by inducing electrochemical reactions of a fuel gas and an oxygen-containing gas is provided. An oxygen-containing gas inlet pipe 3, a coolant water inlet pipe 4, a fuel gas outlet pipe 5, a coolant water outlet pipe 6, a fuel gas inlet pipe 7, and an oxygen-containing gas outlet pipe 8 are connected to the fuel cell stack 2 through a fuel cell manifold 9.
The oxygen-containing gas inlet pipe 3 supplies the oxygen-containing gas to the fuel cell stack 2, the coolant water inlet pipe 4 supplies the coolant water to the fuel cell stack 2, and the fuel gas outlet pipe 5 discharges the fuel gas from the fuel cell stack 2. The coolant water outlet pipe 6 discharges the coolant water from the fuel cell stack 2, the fuel gas inlet pipe 7 supplies the fuel gas to the fuel cell stack 2, and the oxygen-containing gas outlet pipe 8 discharges the oxygen-containing gas from the fuel cell stack 2.